1. Field of the Invention
The present invention relates to a bag for an inflatable belt of an inflatable belt device for protecting a vehicle occupant during a vehicle collision, wherein the bag is arranged in a portion of a seat belt and can be inflated with gas introduced from a gas generator.
2. Description of the Related Art
An inflatable belt device of this type has been developed by the present applicant and is disclosed in Japanese Patent Application H09-236903. The device includes an inflatable belt capable of being inflated and a gas generator for supplying gas into the inflatable belt to inflate it. The inflatable belt includes a bag folded in a band-like configuration and a cover enclosing the bag. The cover is hard to stretch in the longitudinal direction of the inflatable belt and is able to stretch in the width direction of the inflatable belt. In addition, when the inflatable belt inflates, the length of the cover in the longitudinal direction shrinks due to the stretching of the cover's width.
This inflatable belt device is shown in FIGS. 4(a)-6(d). As shown in FIGS. 4(a) and 4(b), the passenger protective device includes a shoulder belt 2 extending diagonally from the right side to the left side of a passenger, a lap belt 3 extending from the right side to the left side of the passenger, a buckle 4 fixed to, for example, a vehicle floor, a tongue 5 to be inserted into and engaged with the buckle 4 when the passenger wears the belt, and an intermediate guide 6 for guiding the shoulder belt 2.
The shoulder belt 2 includes a normal webbing 2A, which is the same as a typical conventional seat belt, and an inflatable belt 2B connected to an end of the webbing 2A. The webbing 2A is slidably hung in the intermediate guide 6. The other end of the webbing 2A is connected to a shoulder belt retractor 7 with an emergency locking mechanism (ELR), which is fixed to the vehicle body. The webbing 2A is arranged such that it is wound into the shoulder belt retractor 7.
The inflatable belt 2B is positioned so that it contacts the passenger and is connected to the tongue 5 at an end opposite to the end connected to the webbing 2A. The lap belt 3 is composed of a normal webbing, which is the same as a typical conventional seat belt, having one end is connected to the tongue 5 and the other end connected to a lap belt retractor 8 (ELR), which is fixed to the vehicle body. A gas generator 9 is connected to the buckle 4. The gas generator 9 is actuated in emergency situations, e.g., vehicle collisions, to generate high-pressure gas. The tongue 5 and the buckle 4 are each provided with passages for introducing gas from the gas generator 9 into the inflatable belt 2B.
As shown in FIG. 5(a) through FIG. 6(d), the inflatable belt 2B includes a bag 10 and a cylindrical knit cover 12 enclosing the bag 10. The bag 10 is shaped such that that the parts corresponding to the chest and abdomen of the occupant are wider than the other parts. As shown in FIG. 5(b), the wider part is folded to shape the bag 10 into a long band-like configuration and the bag is sewn such that there is a stitching seam 11.
The knit cover 12 is supplely stretchable in its width direction, but is hard to stretch in the longitudinal direction of the belt.
The inflatable belt 2B and the lap belt 3 are connected to a tongue 5. The knit cover 12 is connected to both the webbing 2A and the tongue 5 and is designed to withstand a tension load applied to the inflatable belt.
When the gas generator 9 is actuated while the tongue 5 is latched to the buckle 4, the inflatable belt 2B is inflated. During inflation, the knit cover 12 shrinks in the longitudinal direction so that the length of the inflatable belt 2B is shortenedand the inflatable belt 2B thus becomes in close contact with the occupant, thereby securely protecting the occupant.
In the inflatable belt device, as the gas generator is actuated to inflate the inflatable belt, the cover is also inflated. Because the cover is hard to stretch in the longitudinal direction of the inflatable belt, the length of the cover is shortened during its inflation. As a result, the length of the inflatable belt is shortened so that the inflatable belt strongly fits the occupant. Therefore, the occupant can be securely protected.
Such a bag of an inflatable belt device should have a sufficiently small thickness in the folded state; i.e., it should be thin itself, and should be very smooth to minimize the frictional resistance with the knit cover during deployment of the inflatable belt and to enable the belt to deploy smoothly so that the belt inflates quickly.